One of the basic developmental processes in higher eukaryotes is the activation of specific sets of genes in each tissue and the repression of all other genes. In the pathological state of cancer, dramatic alterations occur in the phenotypes of tissues, suggesting a derangement in the specified pattern of gene expression. The long term goals of this study are to find the mechanisms of tissue specific gene expression and how it is affected in cancer. An excellent model for studying these processes is the human alkaline phosphatase (AP) gene system. The placental isoenzyme (PLAP) is encoded by the PLAP-1 gene, and the intestinal isoenzyme (IAP) by the closely related (90 percent homologous) IAP gene. A third gene, the PLAP-2, is 95 percent homologous with the PLAP-1 gene and may encode the 'PLAP'Like' AP that is overproduced in testicular carcinomas. Cell lines that express specifically either the PLAP-1 gene or the IAP gene will be studied to find out whether the differential expression is controlled by transcriptional or posttranscriptional mechanisms. Similar studies will be done with cell lines that appear to express the PLAP-2 gene. Nucleotide sequences that are responsible for differential expression will be found by transfection of the cells with suitable promoter fusion genes followed by site-directed mutagenesis. Ultimately, this work will lead to the isolation of cellular factors that interact with AP gene regulatory sequences (or with AP transcripts) to mediate tissue-specific gene expression. Some human tumors aberrantly express alkaline phosphatase activity. This is most evident in testicular carcinomas (seminomas), where greater than 90 percent of patients have elevated levels of serum PLAP-like enzyme. The PLAP-like enzyme may be the product of the PLAP-2 gene, or perhaps arises from posttranscriptional modification of the PLAP-1 transcript. To test these possibilities, mRNA from testes, seminoma and cell lines producing the PLAP-like enzyme will be analyzed by cDNA cloning and Northern blotting with gene-specific probes. These studies will ultimately lead to an understanding of how tissue specific gene expression is altered in cancer.